A trimethylsilyl group (abbreviated TMS) is a functional group in organic chemistry. This group consists of three

methyl In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...

groups bonded to a silicon atom minus;Si(CH₃)₃ which is in turn bonded to the rest of a molecule. This structural group is characterized by chemical inertness and a large

molecular volume The Van der Waals surface of a molecule is an abstract representation or model of that molecule, illustrating where, in very rough terms, a surface might reside for the molecule based on the hard cutoffs of Van der Waals radii for individual at ...

, which makes it useful in a number of applications. A trimethylsilyl group bonded to a methyl group forms tetramethylsilane, which is abbreviated as TMS as well. Compounds with trimethylsilyl groups are not normally found in nature. Chemists sometimes use a trimethylsilylating

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

to derivatize rather non-volatile compounds such as certain

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

s, phenols, or

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

s by substituting a trimethylsilyl group for a hydrogen in the

hydroxyl group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy g ...

s on the compounds. This way trimethylsiloxy groups minus;O-Si(CH₃)₃are formed on the molecule. A couple of examples of trimethylsilylating agents include trimethylsilyl chloride and bis(trimethylsilyl)acetamide. Trimethylsilyl groups on a molecule have a tendency to make it more volatile, often making the compounds more amenable to analysis by

gas chromatography Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, ...

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...

. An example of such trimethylsilylation is mentioned in the

Brassicasterol Brassicasterol (24-methyl cholest-5,22-dien-3β-ol) is a 28-carbon sterol synthesised by several unicellular algae (phytoplankton) and some terrestrial plants, like rape. This compound has frequently been used as a biomarker for the presence of ( ...

article. Such derivatizations are often done on a small scale in special vials. When attached to certain functional groups in a reactant molecule, trimethylsilyl groups may also be used as temporary

protecting group A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis. In many ...

s during chemical synthesis or some other chemical reactions. In chromatography, derivitization of accessible silanol groups in a bonded stationary phase with trimethylsilyl groups is referred to as endcapping. In an NMR spectrum, signals from atoms in trimethylsilyl groups in compounds will commonly have chemical shifts close to the tetramethylsilane reference peak at 0 ppm. Also compounds, such as high temperature silicone "

stopcock A stopcock is a form of valve used to control the flow of a liquid or gas. The term is not precise and is applied to many different types of valve. The only consistent attribute is that the valve is designed to completely stop the flow when clo ...

" grease, which have polysiloxanes (often called silicones) in them will commonly show peaks from their methyl groups (attached to the silicon atoms) having NMR chemical shifts close to the tetramethylsilane standard peak, such as at 0.07 ppm in CDCl₃. Otherwise very reactive molecules can be isolated when enveloped by bulky trimethylsilyl groups. This effect can be observed in tetrahedranes.

Super silyl groups

Related to trimethylsilyl groups are "super" silyl groups of which there exist two varieties: A silicon group connected to three trimethylsilyl groups makes a tri(trimethylsilyl)silyl group (TTMSS or TMS₃Si) and a silicon group connected to three tert-butyl groups. The TTMSS group was proposed in 1993 by Hans Bock. With a van der Waals volume of up to 7 cubic angstrom it surpasses the related TIPS group (around 2) and one potential application is its use as a temporary substituent promoting

asymmetric induction In stereochemistry, asymmetric induction (also enantioinduction) describes the preferential formation in a chemical reaction of one enantiomer or diastereoisomer over the other as a result of the influence of a chiral feature present in the sub ...

for example in this diastereoselective one-pot reaction involving two sequential Mukaiyama aldol reactions: : Supersilylapplication

TTMSS can also stand for tris(trimethylsilyl)silane, which is comparable as a chemical reagent to tributyltin hydride without the associated toxicity concern of

organotin Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. The first organotin compound was diethyltin diiodide (), discovered by ...

and tributyltin compounds. The reagent is employed in

radical reductions Radical may refer to: Politics and ideology Politics *Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...

, hydrosilylation and consecutive radical reactions.

Alcohol protection

In organic synthesis, TMS group is used as a

for

alcohols In chemistry, an alcohol is a type of organic compound that carries at least one hydroxyl () functional group bound to a saturated carbon atom. The term ''alcohol'' originally referred to the primary alcohol ethanol (ethyl alcohol), which is ...

Most common protection methods

* Trimethylsilyl chloride (TMSCl) or

trimethylsilyl trifluoromethanesulfonate Trimethylsilyl trifluoromethanesulfonate is a trifluoromethanesulfonate derivate with a trimethylsilyl R-group. It has similar reactivity to trimethylsilyl chloride, and is also used often in organic synthesis. Illustrative reactions A common ap ...

(TMSOTf) and base (i.e. pyridine, triethylamine, or 2,6-lutidine) in

dichloromethane Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odour is widely used as a solvent. Although it is not miscible with ...

* TMSCl and lithium sulfide (Li₂S) in acetonitrile

Most common deprotection methods

* TMS groups are susceptible to cleavage upon treatment with HF-based reagents ** Tetrabutylammonium fluoride (Bu₄NF) in THF ** Fluorosilicic acid (H₂SiF₆) * Treatment with HCl in THF/water solution

References

External links